Core-sampling apparatus



Feb. 25., 1969 PARDUE 3,429,383

CORE-SAMPLING'APPARATUS Filed Sept. 15, 19s? 24 I 35 George b. Para 0e 35 INVEN'IOR.

' BY Qt Afro/mf V United States Patent 3,429,383 CORE-SAMPLING APPARATUS George H. Pardue, Houston, Tex., assignor to Schlumberger Technology Corporation, Houston, Tex., a corporation of Texas Filed Sept. 15, 1967, Ser. No. 667,918 Us. 01. 175 4 Int. Cl. E2lb 49/06 7 Claims ABSTRACT OF THE DISCLOSURE The particular embodiment described herein as illustrative of one form of the invention is a tubular coretaking bullet adapted to be propelled against the adjacent wall of a borehole from which a formation sample is desired. To enhance the penetration of the bullet as well as to minimize the effects of the impact upon the bullet, and forward cutting edge of the bullet is formed to be substantially complementary to the curvature of the borehole wall so all portions of the cutting edge of the bullet will strike the borehole Wall simultaneously.

found that these and other types of core-taking bullets have a fairly short life and sometimes cannot be re-used more than one or two times before becoming unduly deformed or broken. Moreover, when any of the bullets known heretofore are propelled into particularly hard formation materials, their depth of penetration may be somewhat less than might sometimes be desired and the resulting core may not be as suitable as one from a softer formation.

Accordingly, it is an object of the present invention to provide new and improved core-taking bullets that will penetrate further into harder formations and obtain more satisfactory core samples than has been possible heretofore. It is a further object of the present invention to provide new and improved core-taking bullets that can be re-used a significantly greater number of times than any of such bullets known heretofore.

These and other objects of the present invention are obtained by forming the forward cutting edge of a tubular core-taking bullet with a curvature substantially complementary to the curvature of the borehole wall into which the bullet is to be propelled. In this manner, when the bullet is fired, the entire circumference of the forward cutting edge of the bullet will simultaneously strike the formation thereby eliminating unduly concentrated stresses and minimizing possible deformation of the cut-ting edge as has been the case with prior-art bullets.

The novel features of the present invention are set forth with particularity in the appended claims. The operation, together with further objects and advantages thereof, may best be understood by way of illustration and example of certain embodiments when taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a cross-sectional view of formationsampling apparatus including a core taking bullet arranged in accordance with the principles of the present to the central axis of a borehole in which the bullet is to be employed; and

FIGURE 3 is a view similar to FIGURE 2, but with the bullet being rotated 90 about its central axis to better illustrate the present invention.

Turning now to FIGURE '1, a typical core-taking tool 10 is depicted in a borehole 11 and adjacent an earth formation 12 from which one or more core samples (not shown) are to be obtained. Although the borehole 11 will usually contain a well control fluid or so-called mud, it will be understood, however, that the present invention may also be used in dry boreholes. As is customary, the core-taking tool 10 is adapted for suspension in the borehole 11 from a suitable cable (not shown) having one or more electrical conductors therein. The body 1'3 of the tool 10 is an elongated member adapted to carry a number of bullets 14 arranged in accordance with the present invention and spaced along the longitudinal axis of the body.

As shown in FIGURE 1, each of the bullets 14 are slidably disposed in a generally horizontal, lateral bore 15 provided in the tool body 13, with the forward portion of each bullet projecting outwardly from the open forward end of its respective lateral bore. The rearward end of each lateral bore 15 is counterbored to provide a chamber '16 in the tool body 13 that terminates short of the rear surface thereof and receives an explosive 17. A small passage extending from one side of the tool body 13 and terminating in the chamber 1 6 is adapted to receive a typical electrically-responsive igniter 18 which, when actuated, will detonate the explosive 17 confined in the chamber. A suitable electrical conductor (not shown) between the igniter 18 and the conductor in the suspension cable (not shown) completes the electrical circuit. As is custmoary, one or more flexible retrieving wires 19 are connected between the tool body 13 and each of the bullets 14 to permit recovery of the bullets after they have been fired.

Turning now to FIGURE 2, a bullet 14 is shown in the same relative orientation as depicted in FIGURE 1. As seen in FIGURE 2, the bullet 14 is comprised of a substantially cylindrical tubular body 20 having threaded lateral bores. 21 on opposite sides thereof and respectively adapted to receive a threaded connector member (not shown) on the outer end of each retrieving wire 19. One or more ports, as at 22 are provided in the bullet body 20 to discharge well fluids from the central bore 23 of the body as the bullet enters a formation as at 12 (FIG- URE 1). The rearward end of the bullet body 20 is closed by a closure member 24 that is secured in some appropriate manner to the body as by a transverse connecting pin 25. One or more circumferential grooves 26 are provided around the closure member 24 to confine one or more sealing members, such as O-rings 27, for fluidly sealing the rear portion of the bullet 14 within its respective bore 15 to prevent Well fluids from reaching the explosive 17.

The forward portion of the bullet body 20 is particularly formed to provide an enlarged-diameter shoulder 28 having a. flat, forwardly directed face 29 ahead of the ports 22. Just ahead of the flat face 29, the bullet body 20 includes a generally cylindrical portion 30 which terminates upon reaching a reduced-diameter cylindrical nose portion 31 at the forwardmost portion of the bullet body. A frusto-conical annular member 32 is loosely disposed around the intermediate body portion 30 and releasably secured thereon by means such as a typical snap ring 33 partially disposed in a circumferential groove just behind the nose 31. For reasons that will subsequently become apparent, it will be noted from EIGURES'Z and 3 that the outer diameter of the annular member 32 is somewhat greater than the outer diameter of the shoulder 28.

It will be realized, of course, that the nose 31 of the body 20 will be the first portion thereof to enter the formation 12 when the bullet 14 is fired. Accordingly, in accordance with the present invention, the forward transverse surface of the nose 31 is appropriately curved, as at 34, to be substantially complementary to the curvature of a typical borehole in which the bullet 14 may be used. Thus, the axis of revolution about which the curved terminal surface 34 is formed will be substantially coincidental with the central axis 35 of the borehole 11 as shown in dotted lines in FIGURE 2. -It will be appreciated from a comparison of FIGURES 2 and 3 that the axis of rotation of the terminal surface 34 is perpendicular to the central axis 36 of the bullet 14. Stated another way,

it will be realized that this curved terminal surface 34 can be defined as being the intersection of a cylinder of the diameter of the nOSe portion 31 with the internal wall of a cylinder of the same diameter as the borehole 11 when the longitudinal axis (as at 36) of the smaller cylinder is perpendicular to the longitudinal axis (as at 35) of the larger cylinder.

In this manner, with the bullet 14 oriented as shown and with its central axis 36 perpendicular to the axis 35 of the borehole 11, when the bullet first strikes the wall of the borehole, all portions of the curved terminal surface 34 will simultaneously contact the bore-hole wall. Thus, in contrast to what occurs as a typical flat-nose bullet (as shown in Patent No. 3,101,797 for example) strikes the curved borehole wall, the full circumference of the curved terminal surface 34 will be simultaneously subjected to the impact forces and all portions of the nose 31 will be uniformly stressed rather than being unevenly stressed as in the case with a typical flat-nosed bullet.

It has been found that by curving the terminal surface 34 of the nose 31 of the bullet 14, the life of such a bullet is greatly increased in comparison to typical fiat-nosed bullets that are subjected to the same conditions. For example, when the bullets 14 of the present invention and fiat-nosed bullets (not shown) that were otherwise identical were fired against identical test targets, the flat-nosed bullets on the average failed after only two shots but the bullets of the present invention did not become unusable until after 5 to 6 shots. It is quite evident, therefore, that the bullets 14 of the present invention represent a significant advance in the art. It was also noted during these tests that the cores recovered by the bullets 14 were much less disturbed than the cores obtained by the typical flat-nosed bullets.

In a typical operation, one or more of the bullets 14 are arranged in the bores 15 in the tool body 13 ahead of the explosives 17 in the chambers 16. The igniters 18 are inserted and their respective conductors are approximately connected. Once the tool has reached the desired depth in the borehole 11, one or more of the igniters 18 are energized as required and a corresponding number of the bullets 14 are explosively propelled from their respective bores 15. Where, for example, the formation 12 is relatively soft, after the nose portion 31 of a bullet 14 has penetrated the wall of the borehole 11, the retaining ring 33 thereon will contact the formation and be torn or stripped from its retaining groove. Then, as the bullet 14 progresses further, the annular member 32 Will tend to enlarge the resulting cavity in the formation. The increased diameter of the annular member 32 in relation to the diameter of the nose portion 31 will also serve to slow the bullet 14 and prevent it from being driven too deeply into a softer formation 12. Thus, when the tool 10 is retrieved, since the annular members 32 are now free, the body 20 of each bullet 14 will be easily returned through the enlarged cavity in the formation 12 to the borehole 11, with the annular members usually being left behind. It will be noted that one or more grooves 37 are cut across the enlarged shoulder 28 to insure that the hydrostatic pressure in the borehole 11 will be equalized across at least the annular member 32 once the bullet 14 is imbedded in the formation 12. Thus, should the nose portion 31 be sealingly imbedded in the formation 12, any pressure differential tending to otherwise hold the bullet 14 in place will be acting only across the effective cross-sectional area of the nose.

Generally, when the bullets 14 of the present invention are fired into a relativelyhard formation 12, their penetration will not be so great that the annular members 32 will burrow into the formation. This poses no particular problem, however, since the length of the nose portions 31 of the bullets 14 is sufficient to capture an adequate formation sample. As previously noted, the curved terminal surface 34 will result in a more uniform initial entrance into the formation 12 so that a betterforrned core will be cut. Moreover, as already pointed out, the curved terminal surfaces 34 allows the bullets 14 to penetrate into harder formations further than has been possible heretofore with typical flat-nosed bullets.

Accordingly, it will be appreciated that the new and improved bullets of the present invention represent a considerable improvement over the prior art. By curving the transverse forwardmost terminal surface of the nose portion of these bullets to substantially complement the curvature of the borehole wall against which they are to be fired, all circumferential portions of the nose of the bullets of the present invention will strike the borehole Wall simultaneously. Thus, by virtue of this simultaneous contact, impact stresses on the bullet nose will be uniformly distributed to reduce the effects of the impact on the bullet as well to significantly increase the depth to which the bullet will penetrate therein and obtain more complete and undisturbed samples.

VWaile a particular embodiment of the present invention has been shown and described, it is apparent that changes and modifications may be made without departing from this invention in its broader aspects; and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

What is claimed is:

1. Apparatus adapted for obtaining core samples from earth formations traversed by a bore hole with a curved wall and comprising: a support adapted for reception in a borehole; a coring bullet carried on said support and having a forwardly-opening cavity adapted to receive an earth formation sample, said cavity being terminated by a forward wall-engaging end surface having a curvature substantially complementary to that of a curved borehole wall and adapted for obtaining a sample from such a wall upon impact therewith; means on said support adapted for propelling said bullet from said support and against a borehole wall to obtain a sample therefrom; and means interconnecting said bullet and said support and adapted for retrieving said bullet from a borehole after said bullet has been propelled from said support.

2. Apparatus adapted for obtaining core samples from earth formations traversed by a borehole with a curved wall and comprising: a support adapted for reception within a borehole; a tubular coring bullet carried on said support and having a curved forward end surface facing the wall of such a borehole and substantially complementary to the curvature thereof; means on said support adapted for propelling said bullet from said support and impacting its said forward end surface against such a borehole wall to obtain an earth formation sample therefrom; and means interconnecting said bullet and said support and adapted for retrieving said bullet whenever said support is removed from a borehole.

3. The apparatus of claim 2 wherein said bullet is adapted for propulsion along a longitudinal axis substantially perpendicular to such a borehole wall.

4. The apparatus of claim 3 wherein said curved forward end surface is formed about an axis of revolution substantially perpendicular to said longitudinal axis and intersecting said longitudinal axis at a point to the rear of said forward end surface.

5. A core-taking bullet comprising: a rigid body member having a forwardly-opening axial bore therein along the longitudinal axis of said body member and adapted for receiving samples of earth formations cut away by said bullet, formation-cutting means on the forward portion of said body member including a curved formationcutting forward end surface formed thereon about an axis of revolution substantially perpendicular to said longitudinal axis and intersecting said longitudinal axis at a point to the rear of said forward end surface.

6. The core-taking bullet of claim 5 wherein the radius of curvature of said forward end surface is substantially equal to the radius of a borehole in which said bullet is expected to be used.

7. The core-taking bullet of claim 5 wherein said body member is a tubular cylinder and further including means on said body member for closing the rearward end of said axial bore, and means on said body member adapted for attachment to connecting means on a support carrying said bullet.

References Cited UNITED STATES PATENTS 2,509,608 5/1950 Penfield 175 77 X 3,072,202 1/1963 Brieger l7577 X 3,101,797 8/1963 Brieger l754 3,273,659 9/1966 Reynolds 166l0 0 X 3,347,322 10/1967 Lanmon 166-400 X DAVID H. BROWN, Primary Examiner. 

